The invention relates to an optical recording medium inscribable by a radiation beam, containing control information indicative of a recording process by which information can be recorded on the information carrier, the control information comprising values of recording parameters for the recording process.
Such a recording medium is known from EP-A-0 397 238 (PHN 12.925). This information carrier is a disc of an optically inscribable and readable type such as, for example, a Compact Disc Write Once (CD-WO), compatible with media of the CD class, and has a prerecorded track portion, a so-called pregroove. The pregroove is intended for recording optically readable patterns in accordance with the recording process, which patterns represent information. The pregroove is furthermore modulated with an auxiliary signal which contains address codes and control information. The control information comprises data useful for optimizing the recording process, such as the write power level required for recording.
An optical recording apparatus, set up for recording information on such a medium, can read the control information from the medium and adjust its recording parameters in accordance with the values recorded on the medium in order make a reliable recording of the information in the form of marks on the medium. Recording parameters are understood to be parameters which directly control the recording process. If the apparatus records information by modulating the power level of the radiation beam, these parameters may include one or more speeds of recording, power levels of the radiation beam used during the recording, such as a write power level, a bias power level, the duration of a first, intermediate and last pulses of a series of pulses used for writing a mark on the medium and duty cycles of these pulses. Several values of each parameters for specific recording speeds may be recorded. If the recording process includes erasure of previously recorded information either by direct overwrite or in a separate pass, the parameters may also include parameters related to the erase process such as the erase power.
Read parameters are understood to be parameters derivable from signals obtained when reading the information on the medium and which are useful for optimizing the value of one or more recording parameters. In general, a method for adjusting a specific recording parameter will involve recording a series of test patterns on the medium, each pattern having a different value of the recording parameter, measuring the read parameter of each pattern, and determining the optimum value of the recording parameter from this information. Examples of read parameters are the maximum value of a read signal, the modulation of a read signal, the reflection of the medium, the jitter of a read signal and the error rate of information recovered from the read signal.
European patent application no. 0 737 962 discloses an optical recording apparatus which does not require control information from an optical medium in order to set its write power level for recording information on the medium. Instead, the apparatus records a series of test patterns, each with increasing write power, on the medium. Next, it derives the modulation of each pattern from a read signal portion corresponding to the pattern. It calculates the derivative of the modulation as a function of write power and normalises the derivative by multiplying it by the write power over the modulation. The intersection of the normalised derivative with a preset value determines a write power level suitable for recording on this medium. The method thus uses the write power as recording parameter and the read signal modulation as the read parameter. This procedure for setting the optimum write power takes the different characteristics of the media into account by measuring the modulation of test patterns written on the media. Moreover, the method is independent of the specific recording apparatus used because of the normalised derivative employed in the procedure. The derivative is insensitive for apparatus parameters such as the numerical aperture of the objective lens for focusing the radiation beam on the medium, the intensity distribution over the radiation beam and the size of the spot formed by the radiation beam. The known method is designed to provide a proper setting of the write power level for each combination of recording apparatus and medium. However, experiments have revealed that the known method does not result in a proper write power level for all combinations of apparatuses and media.
The above citations are hereby incorporated in whole by reference.